Use your finger to follow along! It sounds childish, but there's a reason children do it, because it's an easy way to boost comprehension and reading speed.
I also use audiobooks to listen while I read, for particularly challenging stuff.
Besides that, just practice. If something is too hard, ease into it with something a little easier. Reading is just like any other skill, you have to practice it and get better. Try harder and harder things to train your muscles.